Workers at President Trump’s Washington hotel have voted to join one of America’s leading labor unions, setting the stage for potentially tense labor negotiations at one of Trump’s most high-profile businesses a few blocks from the White House.

About 40 housekeepers and guest-room workers at the Trump International Hotel Washington voted last week to join Unite Here Local 25, a chapter that represents 6,500 hospitality workers across the Washington area, a union executive said.

The vote, the first major unionization effort of Trump-company workers following Trump’s inauguration, again highlights the thorny entanglements facing the businessman-president, who has given corporate management responsibilities to his children but has refused to divest from his business interests.

The president will be able to appoint the top members of the National Labor Relations Board, which rules on labor disputes, including the bitter months-long battle last year between Trump and workers at his Las Vegas hotel.

Trump’s company agreed to end that dispute in December by negotiating with Unite Here’s Nevada affiliate and offering new benefits to hundreds of the Vegas hotel’s housekeepers, cooks and other employees.

Trump Organization representatives did not respond to requests for comment. Trump Hotels chief executive Eric Danziger said in a statement last month that the company and the D.C. union shared a mutual goal to make the Washington hotel “one of the finest hotels in the world.”

Trump’s duel with the Vegas union during his campaign spurred members to protest his hotels and campaign events nationwide. During the days after his election, Trump fired off tweets slamming the leader of an Indianapolis steelworkers union who had questioned Trump’s taking credit for saving jobs at a Carrier plant.

But Trump has also sought to court unions since his election. Trump this month convened half a dozen construction-union leaders for an hour-long talk at the White House and hosted the head of America’s biggest union federation, the AFL-CIO, for a meeting at Trump Tower.

White House press secretary Sean Spicer on Tuesday pointed to how the president had “brought unions together” to rebut a question during a press briefing about whether Trump’s language was divisive.

Unite Here, whose members largely include hotel, food-service and casino employees, was not part of Trump’s early union talks, and they could remain a potential opponent of Trump’s policies. The union marched during the Women’s March in Las Vegas the day after Trump’s inauguration, saying in a statement, “We will fight and ensure that all people who make this country great have a seat at the table.”

John Boardman, executive secretary and treasurer of the Unite Here’s D.C. affiliate, said 95 percent of Trump housekeepers and guest-room workers voted to join the union, which will push to adopt the same benefits and protections offered to workers at other downtown Washington hotels.

Another 80 bartenders, servers, porters and other Trump hotel workers are expected to vote on union membership within the coming months.

The union will serve as the workers’ bargaining agent with the Trump company, said Boardman, who expects contract negotiations to begin “very soon.” He said he thinks the company “would like to reach an agreement” and that negotiations would end fairly quickly.

The union, Boardman said, hopes to cover Trump hotel workers under a broader multi-hotel agreement providing for pension plan increases and raises for workers, with housekeepers and dishwashers’ annual income rising to $52,000 by the end of the five-year contract.

Trump leases the Pennsylvania Avenue building, the historic Old Post Office Pavilion, but it is owned by the federal government. Trump owns a 76 percent share in the hotel project, with most of the remaining stake divided between his children Donald Jr., Eric and Ivanka, lease documents show.

The luxury hotel opened its doors this fall and quickly became a fixture in Trump’s campaign, hosting news conferences and lavish parties for his inauguration. Trump said this month he would put his sons in charge of managing his businesses, but that he would retain his ownership stakes.

The hotel has become a key vulnerability and major distraction for Trump in the first days of his presidency. A liberal watchdog group, Citizens for Responsibility and Ethics in Washington, filed a lawsuit last week alleging Trump has violated a constitutional clause banning federal officials from accepting payments or gifts from foreign governments.

An attorney for Trump, who has said the case was “without merit,” argued this month that the constitutional ban, under the “emoluments clause,” does not apply to hotel stays and other fair-market transactions.

The attorney also pledged that Trump would donate hotel profits from foreign business and government clients to the U.S. Treasury. Neither Trump nor representatives of his private company, the Trump Organization, have released details on how those payments would be tracked, collected and disbursed.

The Department of Justice will defend Trump in the lawsuit. A DOJ spokeswoman said, “The Justice Department is reviewing the complaint and will respond as appropriate.”